The purpose of this proposal is to understand the effects of chronic exercise on resting blood pressure and its regulation in trained populations. The subject is as controversial as it is important because an equal number of positive and negative results have been published and because more than 20 million Americans are hypertensive. Our animal data indicates training will reduce; but, not normalize resting pressures in adult hypertensive groups; attenuate the rise in pressure with borderline hypertensives (DOCA) and lower values in normal populations. To extend these observations and to understand the responsible mechanisms, short and long term investigations with normal, borderline hypertensive and genetic hypertensive rats are planned to show the influence of training when exercise is scheduled 1) soon after weaning, 2) after the animals are one year or older, 3) when the dosages of the antihypertensive agents have been reduced by 50% and 75%, and 4) after genetic hypertensive rats have been sympathectomized by chemical means. Training will be accomplished using exercise schedules that require an oxygen consumption that represents between 65-80% of the maximum capacity of the animals. Besides measurement of resting pressures, data will be collected on the effects of carotid sinus nerve stimulation, reflex responsiveness after lower body negative pressure with different PO2 levels, "reactivity" changes in perfused hind limb preparations and on the effects of different chemical (Ca ions, Ba ions or pharmacological (NE, E, tyramine, isoproterenol) agents on isolated vessels. Histological sections from tail arteries will be prepared for the determination of wall/lumen ratios using the computer capability of the Quantimet 720 automatic image analyzer. Emerging from these studies should be new and interesting information on the importance of chronic exercise in the management of hypertension.